As the major seafood supplier in Asia, Hong Kong faces the challenges of water and food security. In particular, the excessive growth of phytoplankton can cause rapid oxygen depletion, discoloration in water, shellfish poisoning and massive fish kills. Therefore, water quality monitoring and forecasting is important. Water transparency is a significant parameter in water quality monitoring and forecasting model. Secchi depth and light extinction coefficient are two major parameters of water transparency.

The light attenuation in coastal water is caused by absorption and scattering of particles including phytoplankton, suspended material, organic matters and water itself. The relationships between the light extinction and related water quality parameters have been studied in various wate...[ Read more ]

As the major seafood supplier in Asia, Hong Kong faces the challenges of water and food security. In particular, the excessive growth of phytoplankton can cause rapid oxygen depletion, discoloration in water, shellfish poisoning and massive fish kills. Therefore, water quality monitoring and forecasting is important. Water transparency is a significant parameter in water quality monitoring and forecasting model. Secchi depth and light extinction coefficient are two major parameters of water transparency.

The light attenuation in coastal water is caused by absorption and scattering of particles including phytoplankton, suspended material, organic matters and water itself. The relationships between the light extinction and related water quality parameters have been studied in various water regions. However, there is little systematic investigation on light extinction in Hong Kong coastal waters. The long-term water quality data (1986-2017) has been used to study the spatial and temporal variability of light extinction characteristics at various coastal locations in Hong Kong. It is found that in Tolo Harbour light extinction is mainly affected by Chlorophyll-a (Chl-a), while in Victoria Harbour suspended solids (TSS) is more important. The major infrastructure projects (e.g. Harbour Area Treatment Scheme) have obvious effects on water transparency. A multiple linear regression model to predict Secchi depth as a function of Chl-a, TSS and non-algal BOD₅ is developed. An artificial neural network model is also developed for two stations in Tolo Harbour and Victoria Harbour.

Based on the contrast theory and image analysis, a remotely controlled system for field measurement of light extinction is developed and installed at Yim Tin Tsai Fish Culture Zone, Tolo Harbour. It collects light intensity data and digital photos, which can be instantly accessed in the HKUST lab. The result shows that the remotely controlled system is applicable to predict light extinction of water on a daily basis.